1. Field of the Invention
The present invention relates to apparatus for and methods of monitoring functioning of explosive devices. More particularly, the invention relates to apparatus for and methods of monitoring functioning of explosive devices utilizing lithium niobate crystals as detonation monitors.
2. Technical Considerations and Prior Art
A general trend in configuring devices for monitoring explosions is to utilize optical instrumentation. However, optical devices are relatively large, expensive and complex and require relatively sophisticated systems for their operation. If optical systems are utilized, the amount of detonator explosive material must be increased to achieve sufficient signal levels. This has serious implications for explosive containment and can cause collateral damage to other components. Moreover, at low energy levels optical monitors are entirely passive and, therefore, cannot be excited for self-check purposes to determine if the monitoring device is functioning.
There has been investigation into using the piezoelectric effect of crystal devices for monitoring detonations. However, piezoelectric materials such as barium titanate (BaTiO.sub.3), lead zirconate titanate (PZT), and crystals such as quartz cannot withstand high stress levels in excess of hundreds of kilobars reliably enough to produce a piezoelectric response for generating a readable output current.
U.S. Pat. No. 3,714,476 of Epstein discloses a lithium niobate crystal arranged at a particular angle for use as a compression accelerometer over a long period of time at elevated temperatures. This patent is typical of lithium niobate devices useful for low signal applications but incapable of providing an output at the pressures for which the present invention is designed.
U.S. Pat. No. 3,307,052 of Neilson, et al. uses a disk of x-cut crystal to measure the effect of a detonation or other impact. This device is restricted to monitoring much lower pressures than applicants' invention.
Monitoring the time explosions has typically been restricted to detection times of tens of nanoseconds. No known prior art detector is fast enough to provide a response within a few nanoseconds that more accurately represents the initiation of the explosion.